This invention relates to the type of blow molding machine in which an indexing plate rotates intermittently to move core rods carried by an attached head to an injection station where molten parisons are applied to core rods. The next movement of the head carries the rods to a blowing station at which the parisons on the core rods are blown to the shape of the cavities of the mold at the blowing station. The last station has cooled articles stripped from the core rods.
While three stations are basic for blow molding machines, some machines have additional intermediate stations for special operation such as temperature control, coating and other operations. The invention is an improvement that can be used for machines having any number of stations; but it will be described as applied to a basic three-station machine.
The head that is carried by the indexing plate is a polygon, in plan view, and face blocks on sides of the polygon hold core rods projecting at right angles to the sides of the face block in directions for projecting into molds at the injection and blowing stations. Molds on the machine have to be changed for every different product and size of product; and usually core rods have to be changed also. When the molds open, the indexing plate and the head connected with it rise and lift the core rods clear of the lower, fixed mold section, and the indexing plate and head turn far enough to move the core rods to the next station.
While longer molds and longer core rods can be used to make longer parts, every conventional machine has a limit on the length of core rods it can use without having the core rods strike some fixed part of the machine when the indexing plate turns angularly to move the core rods to the next station. This invention makes possible a greater range of sizes of the parts that can be made on the machine so that one machine can obtain a variety that would formerly require two or more machines of different size.
The basic concept of this invention is to provide a small size of indexing plate so that a small head on the indexing plate can support core rods which are set back nearer to the center of rotation of the indexing head, and this permits the use of longer rods and larger molds without having the core rods strike the fixed structure of the machine when the indexing head turns. For smaller articles, larger heads are placed on the indexing plate, and the larger heads have longer side faces and can accommodate more core rods, though the core rods have to be shorter in order to clear fixed parts of the machine when the indexing plate rotates the head to the next operational station. Air passages, valve-operating mechanisms and other controls of the different size heads are constructed so that they register with corresponding parts of the basic head so that no elaborate circuit changes are required.
The invention also includes some improvements in the air connections, indexing registration mechanism, and cams for operating air valves for the blowing operation.
Other objects, features, and advantages of the invention will appear or be pointed out as the description proceeds.